Cable networks are communication systems that typically employ coaxial cables to carry broadband signals between a centralized head end and a plurality of customer premises devices. In addition to coaxial cables, many conventional cable networks also include fiber optic lines. Such networks are sometimes called hybrid fiber coax (HFC) networks.
Cable networks have historically been used primarily for the delivery of the television program signals. To this end, a cable network head end typically broadcasts a broadband multi-channel television signal to a plurality of subscribers through a hierarchical interconnection of coaxial cable and/or fiber optic lines which is often referred to as the cable plant. The multi-channel television signal is typically composed of a plurality of different program signals conveyed over separate frequency channels, each channel occupying an approximately 6 MHz wide subband of the overall broadband signal.
While cable service providers have been broadcasting analog NTCS standard television signals for years, they are increasingly converting to digital television signal broadcasting to take advantage of better cost/service ratios. Another increasing trend in cable networks is the addition of two-way high-speed digital data communication. A customer may thus use its cable network connection to obtain both television broadcast programming and to access the Internet for electronic mail, downloads, and browsing. Additionally, an increasing number of HFC networks are also being configured to support a specialized form of digital telephone service known as Voice over Internet Protocol (VoIP). Thus, in addition to reliable downstream data transmissions from cable network head ends to respective subscriber sites, many of the newer and emerging digital services also require increasingly reliable upstream data transmissions from subscriber sites to their respective cable network head ends.
Coaxial cables and connectors are designed to be shielded and prevent over-the-air signals from mixing into the signals carried over the center conductor; however, electromagnetic noise, i.e. ingress, from common external devices, such as hair dryers, washing machines, vacuum cleaners, blenders, bread makers, remote control cars, cordless phones, ham radio, machinery, microwave ovens, at or near the same frequency as desired signals, can dramatically reduce the reliability of upstream data transmissions in a cable network. Coaxial home wiring networks are particularly susceptible to ingress noise if the shielding, connectors, or terminations are substandard or damaged.
The hierarchical nature of the typical cable plant tends to increasingly concentrate and amplify ingress in the return path, i.e. the frequency band used for upstream communications, typically occupying about 5 MHz to 45 MHz under United States standards or about 5 MHz to 65 MHz under European standards, as data flows from the subscriber sites to the head end. Without proper precautions, the resulting signal-to-noise ratio (SNR) at the head end can drop low enough to significantly impair the head end's ability to decode messages from subscriber sites.
Determining specifically what should be done to harden a cable network against ingress typically involves field-testing, to locate points of vulnerability and quantify relative degrees of susceptibility in the return path. Once a vulnerable point is located, steps can be taken to sufficiently harden the affected network branch and/or node against ingress. In some cases, the remedy may be as simple as replacing a chaffed cable or tightening a loose connector to provide sufficient electromagnetic shielding through the affected branch and/or node.
Cable service providers have often used handheld signal measurement equipment to help diagnose various communications problems and perform network analyses. However, historical ingress test apparatuses and methods have required dedicated radio frequency (RF) test signal generating features. Generating dedicated RF test signals has been undesirably costly and complex. Moreover, generating dedicated RF signals can pose undesirable challenges in that return path frequencies typically overlap with commercial aviation bands, and thus the dedicated RF test signals must be generated and used in ways that avoid high power broadcasting and/or leakage that may interfere with aviation communications. Additionally, apparatuses and methods including dedicated test signals have been undesirably complex and time consuming for technicians to setup and operate in the field.
The problem for network operators is complicated by the fact that noise sources are neither always present nor constant in level or frequency. At the time of installation or troubleshooting of services, noise sources may not be present and as such the measurement of ingress noise on the cable plant will be low or not present, even if the coaxial plant has shielding integrity issues. Since most installations are performed during the daytime, when the homeowners and their neighbors are at work, i.e. when there is the lowest level of noise sources turned on in the home, technicians may be unaware of the potential problem of ingress noise.
Accordingly, services can be installed and working within acceptable levels during the installation, however, at a later time when off-air noise sources are turned on, the services may be affected. The net result is repeat service calls and/or unhappy and dissatisfied customers.
The challenge is to proactively identify and locate poorly shielded cable or connectors in coaxial networks with susceptibility to ingress noise at the time the technician is in the home, so that weak spots in the cable plant can be fixed and thus prevent customer observed service impairments, without the noise and ingress sources being present at the time.